Many materials, techniques and processes are known for replicating various microstructure-bearing surfaces in the form of embossed, cast or molded polymeric articles; see, e.g., J. Applied Physics, Vol. 45, No. 10, p. 4557 (October, 1974). U.S. Pat. No. 4,576,850 describes a method of making shaped articles having replicated microstructured surfaces wherein a fluid, castable, one-part radiation addition-polymerizable, crosslinkable, oligomeric composition fills a mold master and the filled mold is irradiated so as to cause polymerization of the oligomeric composition and form the desired article. The articles are monolithic, and no adhesive articles are described.
Interpenetrating polymer networks (IPNs) and semi-interpenetrating polymer networks (semi-IPNs) are known. IPNs result when two polymers are formed from monomers independently in the presence of each other so that the resulting two independent crosslinked polymer networks are physically intertwined but are essentially free of chemical bonds between them. Semi-IPNs are defined as polymer networks of two or more polymers wherein one polymer is crosslinked and one is uncrosslinked. IPNs and semi-IPNs have been described in, e.g., Encyclopedia of Polymer Science and Engineering, Vol. 8; John Wiley & Sons, New York (1984), p. 279-332.
Many examples of IPNs and semi-IPNs are known that are prepared when a mixture comprising two or more monomers that polymerize independently, e.g., by distinct and separate mechanisms such that copolymerization does not occur, is subjected to polymerization conditions for each monomer simultaneously or sequentially. In a number of these cases, the resulting IPN or semi-IPN can be an adhesive composition. In cases of sequential polymerization, the intermediate composition can be an adhesive that is cured (i.e., final polymerization takes place) at a site remote from the first polymerization. U.S. Pat. No. 4,393,195 describes cured, moldable resins comprising a mixture and/or a preliminary reaction product of a cyanate ester, an acrylic epoxy ester and a polyfunctional maleimide that is said to have good adhesive power. Microstructured adhesives are not described. U.S. Pat. Nos. 4,950,696, 4,985,340, 5,086,086, 5,252,694 and 5,376,428, 5,453,450 describe several dual-curable systems comprising two or more separately-curable monomers such as acrylates, cyanates, urethanes, and epoxies, the polymerization products of which are described as being moldable and having adhesive properties. However, no description of the preparation of microstructured adhesives is offered.
U.S. Pat. No. 5,317,067 and Japan Patent Application (Kokai) JP 4 028724 describe a curable epoxy resin -thermoplastic resin mixture that is molded or die-cut into a desired shape, and later heated to cure the epoxy resin component. Representative thermoplastic resins include polyamides, polycarbonates, polyurethanes, polyesters, silicones, phenoxys, poly(vinyl chloride), methacrylates, etc. Formulations are limited to a maximum of 33 weight percent thermoplastic resin.
It is known in the art to mold fully-cured pressure-sensitive adhesives (PSAs) into useful shapes prior to application to a workpiece (see, e.g., U.S. Pat. No. 4,831,070). When a PSA is used, no post-molding curing is required or takes place.
Japan Patent Application (Kokai) JP 6 055572 describes a method of molding a mixture of polycarbonate resin and curable epoxy resin wherein epoxy cure takes place in the mold and the cured mixture is adhered thereto. Delayed cure, or cure after shaping, is not described.
Japan Patent Application (Kokai) JP 55 090549 describes an adhesive resin composition comprising a melt-processable thermoplastic resin containing a curable epoxy resin. The mixture is cast to a desired shape, then heated to cure the epoxy resin.
Japan Patent Application (Kokai) JP 56 049780 describes a curable mixture comprising a curable epoxy resin and a thermosetting acrylonitrile-butadiene copolymer containing reactive carboxyl groups. Heating the cast or molded mixture effects epoxy cure. Alternatively, the mixture can contain an epoxy curative that is only activated at high temperatures after a molded article is formed.
U.S. Pat. No. 5,464,693 describes an adhesive mixture that is cast or molded to a desired shape, then placed on a workpiece and cured by means of a crosslinking agent that is effective only when heated to a temperature higher than that necessary for molding.